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United States Patent |
5,121,137
|
Taki
,   et al.
|
June 9, 1992
|
Color exposing device having optical modulator for producing modulated
light beams for two or more colors
Abstract
A color exposing device for imagewise scanning a photosensitive recording
medium with light beams corresponding to two or more colors, respectively.
The recording medium has photosensitive materials sensitive to respective
bands of wavelength of the light beams, to produce images in the different
colors. The device includes a light source for producing a radiation
including two or more wavelength components whose wavelengths fall within
the respective wavelength bands of the light beams, a color separation
element for separating the radiation ito the wavelength components to
provide the light beams, which are propagated along respective ligh paths,
optical modulators disposed in the light paths, respectively, for
modulating intensities of the light beams, according to respective color
image signals, respectively, to thereby provide respective modulated light
beams, and a scanning arrangement for irradiating a surface of the
recording medium with the modulated light beams along a line, to produce a
line of color images.
Inventors:
|
Taki; Kazunari (Nagoya, JP);
Hattori; Yutaka (Nagoya, JP)
|
Assignee:
|
Brother Kogyo Kabushiki Kaisha (Nagoya, JP)
|
Appl. No.:
|
573806 |
Filed:
|
August 28, 1990 |
Foreign Application Priority Data
| Aug 31, 1989[JP] | 1-224880 |
| Sep 08, 1989[JP] | 1-233915 |
| Oct 31, 1989[JP] | 1-128294[U] |
Current U.S. Class: |
347/232; 347/239; 358/505; 358/515 |
Intern'l Class: |
H04N 001/21 |
Field of Search: |
346/108,107 R,160,1.1
358/75,76,78,296,300,302
|
References Cited
U.S. Patent Documents
4562462 | Dec., 1985 | Egan | 358/75.
|
4862196 | Aug., 1989 | Umeda et al. | 346/108.
|
Primary Examiner: Reinhart; Mark J.
Attorney, Agent or Firm: Oliff & Berridge
Claims
What is claimed is:
1. A color exposing device for imagewise scanning a photosensitive
recording medium with a plurality of light beams corresponding to a
plurality of colors, respectively, said recording medium having a
plurality of photosensitive materials which are sensitive to respective
bands of wavelength of said light beams, to produce images in said
plurality of colors, said device comprising:
a light source for producing a single radiation including a plurality of
wavelength components whose wavelengths fall within said respective bands
of wavelength of light beams;
a color separation element for separating said radiation into said
plurality of wavelength components to provide said plurality of light
beams, respectively, such that said light beams are propagated along
respective light paths;
a plurality of optical modulators disposed in said light paths,
respectively, for modulating intensities of said light beams according to
respective color image signals corresponding to said plurality of colors,
respectively, to thereby provide respective modulated light beams;
scanning means for irradiating a surface of said recording medium with said
modulated light beams, along a line on said surface, to produce a line of
color images in said plurality of colors;
color combining means for combining said modulated light beams into a
composite exposing radiation such that said modulated light beams of said
composite exposing radiation are propagated through respective light paths
leading to said scanning means, optical axes of said light paths leading
to said scanning means being offset with respect to each other so that
scanning spots of said modulated light beams formed on said surface of the
recording medium by said scanning means are offset from each other along a
scanning line in a scanning direction of said scanning means; and
delay means connected to said optical modulators, for delaying a time at
which at least one of said color image signals is applied to a
corresponding at least one of said optical modulators, so that said
scanning spots of said modulated light beams for a same local spot on said
surface of the recording medium are aligned with each other at said same
local spot on said scanning line on the surface of the recording medium.
2. A color exposing device according to claim 1, wherein said light source
comprises a metal halide lamp.
3. A color exposing device according to claim 1, wherein said light source
comprises a metal halide lamp, an elliptical mirror having a focal point
at said metal halide lamp, a concave lens for converting a light produced
by said metal halide lamp and reflected by said elliptical mirror, into
substantially parallel rays, a stop having an aperture, and a conical lens
having a translucent projection which extends through said aperture, said
conical lens receiving said substantially parallel rays and emitting
through said projection said radiation to be incident upon said color
separation element.
4. A color exposing device according to claim 1, wherein said color
separation element comprises a color separation prism which has a
plurality of selectively reflecting films for reflecting therefrom and/or
transmitting therethrough said plurality of wavelength components as said
plurality of light beams such that said light beams are propagated along
said respective light paths.
5. A color exposing device according to claim 1, wherein said color
combining means comprises a color combining prism which has a plurality of
selectively reflecting films for reflecting therefrom and/or transmitting
therethrough said respective modulated light beams such that said optical
axes of said modulated light beams of said composite exposing radiation
are parallel to and offset from each other.
6. A color exposing device according to claim 1, wherein each of said
plurality of optical modulators includes a PLZT crystal which exhibits an
electro-optic effect when said PLZT crystal receives a corresponding one
of said color image signals.
7. A color exposing device according to claim 1, wherein said plurality of
photosensitive materials of said recording medium comprise a first, a
second and a third group of microcapsules which include respective
radiation-curable resins which are cured upon exposure to said respective
bands of wavelength of light beams, and respective chromogenic materials
corresponding to yellow, magenta and cyan which are contained in said
respective radiation-curable resins, said surface of said recording medium
carrying a layer consisting of a mixture of said first, second and third
groups of microcapsules.
8. A color exposing device according to claim 1, wherein said scanning
means comprises a polygon mirror for reflecting said composite exposing
radiation over a predetermined angular range along said line on said
surface of the recording medium, and an f.theta. lens through which said
composite exposing radiation reflected by said polygon mirror is
transmitted, such that a scanning speed of said exposing radiation along
said line is constant.
9. A color exposing device according to claim 8, wherein said color
combining means comprises a plurality of reflecting mirrors for reflecting
at least one of said plurality of wavelength components received from said
color separation element as said plurality of light beams so that optical
axes of said light beams intersect each other such that said light beams
irradiate a same area on each reflecting surface of said polygon mirror.
10. A color exposing device according to claim 1, wherein said color
separation element, said optical modulators and said color combining means
are optically coupled with each other as a single integrated optical
assembly.
11. A color exposing device for imagewise scanning a photosensitive
recording medium with a plurality of signal-controlled modulated light
beams corresponding to a plurality of colors, respectively, said recording
having a plurality of photosensitive materials which are sensitive to
respective bands of wavelength of said light beams, to produce images in
said plurality of colors, said device comprising:
feeding means for feeding said recording medium at a predetermined constant
speed in a feeding direction;
time-sharing modulating means for producing said signal-controlled
modulated light beams at a predetermined time interval which is determined
by a scanning pitch between adjacent scanning lines that are spaced apart
from each other in said feeding direction;
a scanning means for sequentially irradiating a surface of said recording
medium with said modulated light beams at said predetermined time
interval, along each scanning line in a scanning direction intersecting
said feeding direction; and
deflecting means for deflecting said modulated light beams by different
angles in said feeding direction such that lines of scanning spots of the
modulated light beams formed on said surface of the recording medium are
superimposed on each other on the same scanning line, as said recording
medium is fed at said constant speed while said surface is irradiated with
said deflected modulated light beams at said predetermined time interval
for said each scanning line by said scanning means.
12. A color exposing device according to claim 11, wherein said scanning
means comprises a polygon mirror having a plurality of plane reflecting
surfaces for reflecting said plurality of modulated light beams,
respectively, said polygon mirror being rotated about an axis thereof to
deflect the reflected modulated light beams along said each scanning line,
said plane reflecting surfaces being inclined at different angles with
respect to said axis of rotation, so that said plane reflecting surfaces
serve as said deflecting means for deflecting said reflected modulated
light beams in said feeding direction.
13. A color exposing device according to claim 12, wherein said plurality
of modulated light beams consist of three signal-controlled modulated
light beams corresponding to three colors, said plurality of plane
reflecting surfaces of said polygon mirror consisting of three groups of
reflecting surfaces corresponding to said three modulated light beams,
each of said three groups consisting of reflecting surfaces whose number
is a multiple of three, said scanning pitch in said feeding direction is
substantially three times as large as a feeding distance of said recording
medium which corresponds to each one of said three modulated light beams.
14. A color exposing device according to claim 11, wherein said plurality
of photosensitive materials of said recording medium comprise a first, a
second and a third group of microcapsules which include respective
radiation-curable resins which are cured upon exposure to said respective
bands of wavelength of light beams, and respective chromogenic materials
corresponding to yellow, magenta and cyan which are contained in said
respective radiation-curable resins, said surface of said recording medium
carrying a layer consisting of a mixture of said first, second and third
groups of microcapsules.
15. A color exposing device according to claim 11, further comprising a
light source for producing a white light including wavelength components
corresponding to said plurality of colors, and wherein said time-sharing
modulating means comprises means for generating a plurality of color image
signals corresponding to said plurality of colors, at said predetermined
time interval, and an optical modulator for modulating intensities of said
wavelength components according to said color image signals, respectively,
at said predetermined time interval.
16. A color exposing device according to claim 15, wherein said white light
including three wavelength components corresponding to three colors, and
said plurality of color image signals consist of three color image
signals, said time-sharing modulating means further comprising a color
filter which has three filter elements which are selectively placed in an
operating position at said predetermined time interval, said three filter
elements receiving said three wavelength components so as to provide three
modulated light beams.
17. A color exposing device according to claim 16, wherein said optical
modulator is disposed between said light source and said color filter, so
that said three wavelength components are modulated by said optical
modulator before said three modulated light beams are passed through said
three filter elements, respectively.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color exposing device for a recording
apparatus, which is adapted to imagewise scan a photosensitive recording
medium simultaneously or sequentially with two or more modulated light
beams having different wavelength bands corresponding to respective
colors.
2. Discussion of the Prior Art
A conventional color exposing device is shown generally at 130 in FIG. 18,
wherein a photosensitive medium is imagewise exposed to three wavelength
components of light corresponding to three primary colors, i.e., blue,
green and red. The color exposing device 130 has three beam generators
131, 132 and 133 for generating three modulated light beams corresponding
to the three primary colors of light. Each of these beam generators 131,
132, 133 includes a light source 135 such as a halogen lamp which produces
an incoherent radiation in the visible spectrum, a collimator lens 136 for
converging the visible radiation produced by the light source 135, and an
optical modulator 134R, 134G, 134B such as an electro-optic modulator
using a PLZT crystal. The optical modulators 134R, 134G, 134B receive
respective color image signals representative of red, green and blue color
images, and modulate the intensities of the radiations according to the
received color image signals, respectively. The color exposing device 130
uses a dichroic mirror 137 which reflects only the blue component of the
modulated radiation generated by the blue beam generator 131, whereby a
signal-modulated light beam corresponding to the blue color is produced.
The device 130 also uses a dichroic mirror 138 which reflects only the red
component of the modulated radiation generated by the red beam generator
133, to thereby produce a signal-modulated light beam corresponding to the
red color. These blue and red modulated light beams are incident upon a
converging lens 139, with the blue light beam passing through the dichroic
mirror 138. The blue and red components of the modulated radiation
generated by the green beam generator 132 are reflected by the dichroic
mirrors 137 and 138, respectively. That is, only the green component of
the radiation from the generator 132 is transmitted through the dichroic
mirrors 137, 138, as a signal-modulated light beam corresponding to the
green color is received by the converging lens 139. Thus, the
signal-modulated light beams corresponding to the three primary colors of
light are combined into a composite exposing radiation at the converging
lens 139, and is converged at an aperture 140 of a stop. The diameter of
the composite exposing radiation is controlled by the aperture 140 and is
focused by lens 141 on the surface of a photosensitive recording medium on
a platen roll 142. Consequently, a composite scanning spot to imagewise
expose a local portion of the surface of the recording medium is formed.
The scanning spot is moved along a line on the recording medium parallel
to the rotation axis of the platen roll 142 by a suitable beam deflecting
device, as the radiations produced by the light sources 135 of the
generators 131, 132, 133 are modulated according to the respective color
image signals. At the end of scanning of each line on the recording
medium, the platen roll 142 is rotated to scan the next line.
The photosensitive recording medium has three different photosensitive
materials which are sensitive to respective bands of wavelength of the
blue, green and red light beams. Accordingly, a latent image corresponding
to an original image represented by the color image signals applied to the
modulators 134B, 134G and 134R is formed on the photosensitive recording
medium.
In the color exposing device 130 constructed as described above, the three
beam generators 131, 132, 133 use the respective light sources 135.
However, only the appropriate wavelength band of the radiation generated
by each light source 135 is utilized. Therefore, the operating efficiency
of each light source 135 is considerably low, and the exposing device 130
tends to be large-sized and expensive.
Further, it is difficult to align the optical axes of the blue, green and
red modulated light beams accurately with each other when the light beams
are combined into a composite exposing radiation, i.e., white light having
color image information to be reproduced. This difficulty in establishing
the optical axis alignment lowers the manufacturing efficiency of the
device 130, and results in misalignment of the blue, green and red spots
formed on the photosensitive recording medium, for example, in the
scanning direction parallel to the axis of rotation of the platen roll
142.
Where a white laser light source is used in each beam generator 131, 132,
133, the output of the laser source for each of the three primary colors
of light is as low as about several mW. Namely, the intensity of the used
wavelength component of the white laser radiation is relatively low,
whereby a relatively long time is required to expose the recording medium
to the modulated light beams corresponding to the three primary colors.
The color exposing device 130 described above is adapted such that the
photosensitive recording medium is simultaneously exposed to the three
modulated light beams having respective wavelength bands, for each
scanning line. However, each scanning line may be exposed to the three
light beams sequentially or at different times while the recording medium
is fed at a constant speed in the feeding direction which intersects the
scanning line, normally at right angles. In this arrangement, the
recording medium is irradiated along each scanning line three times, first
with a light beam modulated according to the blue image signal for the
line, then with a light beam modulated according to the green image
signal, and finally with a light beam modulated according to the red image
signal.
In the color exposing device adapted for sequential exposure of each
scanning with the three modulated light beams as indicated above, however,
the lines of beam spots formed with the three light beams are more or less
deviated from each other in the feeding direction of the recording medium,
since the recording medium is continuously fed in that direction while the
position of the nominal scanning line on the recording medium is held
constant, for all the three light beams. Consequently, the three scanning
spots formed by the three light beams along each scanning line are not
precisely matched or aligned with each other, whereby the color
reproduction accuracy is deteriorated.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a relatively
small-sized, simple, inexpensive color exposing device for imagewise
scanning a photosensitive medium, which uses two or three wavelength
components of a radiation produced by a single light source.
A second object of the invention is to provide such a color exposing device
which is relatively easy to manufacture in terms of the optical axis
alignment of modulated light beams.
A third object of the invention is to provide a color exposing device
wherein the recording medium is sequentially exposed to two or more
modulated light beams corresponding to respective colors, at a
predetermined time interval while the medium is fed in the feeding
direction, such that the lines of scanning spots formed by the modulated
light beams are superimposed on each other on the same scanning line.
The first object may be attained according to one aspect of the present
invention, which provides a color exposing device for imagewise scanning a
photosensitive recording medium with a plurality of light beams
corresponding to a plurality of colors, respectively, the recording medium
having a plurality of photosensitive materials which are sensitive to
respective bands of wavelength of the light beams, to color images, the
color exposing device comprising: (a) a light source for producing a
radiation including a plurality of wavelength components whose wavelengths
fall within the respective bands of wavelength of the light beams; (b) a
color separation element for separating the radiation into the plurality
of wavelength components to provide the light beams, respectively, such
that the light beams are propagated along respective light paths; (c) a
plurality of optical modulators disposed in the light paths, respectively,
for modulating intensities of the light beams according to respective
color image signals corresponding to the plurality of colors,
respectively, to thereby provide respective modulated light beams; and (d)
scanning means for irradiating a surface of the recording medium with the
modulated light beams, along a line on the surface of the recording
medium, to produce a line of color images in the plurality of colors.
In the color exposing device of the present invention constructed as
described above, the radiation produced by the light source is separated
into two or more wavelength components corresponding to two or more
colors, respectively. The thus obtained two or more light beams are
propagated along respective light paths in which the respective optical
modulators are disposed to modulate the intensities of the light beams
according to respective color image signals corresponding to the
respective colors. The scanning means receive the thus modulated light
beams, to irradiate the surface of the recording medium simultaneously
with the two or more light beams, along a line on the medium, to thereby
produce a line of color images represented by the color image signals.
For example, the light source produces white light which includes three
wavelength components corresponding to red, blue and green colors (three
primary colors of light), and the corresponding three light beams are
obtained by separation of the white light by the color separation element.
The light beams are modulated according to respective red, blue and green
image signals, to provide three corresponding modulated light beams. In
this case, the photosensitive recording medium has three photosensitive
materials (yellow, magenta and cyan) which are sensitive to the three
modulated light beams. Therefore, the single light source is used to
expose the recording medium to the three modulated light beams, for
producing each line of color images according to the image signals
corresponding to the red, blue and green colors (yellow, magenta and
cyan). Accordingly, the present exposing device can be made relatively
small-sized, simple in construction and available at a reduced cost, as
compared with the known device which uses three light sources for the
respective colors.
The color separation element may comprise a color separation prism which
has two or more selectively reflecting films for reflecting therefrom
and/or transmitting therethrough the wavelength components of the
radiation from the light source.
The modulated light beams may be combined by a suitable color combining
element into a composite exposing radiation, which is propagated along a
light path leading to the scanning means, so that the recording medium is
irradiated with the light beams having the respective wavelength bands
corresponding to the two or more colors. The color combining element may
comprise a color combining prism which has a plurality of selectively
reflecting films for reflecting therefrom and/or transmitting therethrough
the respective modulated light beams such that the modulated light beams
are combined into the composite exposing radiation.
Each optical modulator may use a PLZT (PbTiO.sub.3 -PbZrO.sub.3 -La.sub.2
O.sub.3) crystal which exhibits an electro-optical effect when the crystal
receives a color image signal.
The photosensitive recording medium may be a microcapsule type recording
medium which has a layer consisting of a mixture of three groups of
microcapsules corresponding to the primary colors of light. Each group of
microcapsules consists of microcapsules each including a radiation-curable
resin which is cured upon exposure to the modulated light beam having the
appropriate wavelength band, and a chromogenic material (yellow, magenta
or cyan) which is contained in the radiation-curable resin.
The scanning means may comprise a polygon mirror for reflecting the
composite exposing radiation and deflecting the composite exposing
radiation over a predetermined angular range along the scanning line on
the recording medium. The scanning means may further comprise a f.theta.
lens through which the composite exposing radiation reflected and
deflected by the polygon mirror is transmitted so that a scanning speed of
the exposing radiation is constant over the entire length of the scanning
line.
The second object of the invention indicated above may be achieved
according to one preferred form of the present invention, wherein the
color exposing device further comprises color combining means for
combining the modulated light beams into a composite exposing radiation
such that the modulated light beams of the composite exposing radiation
are propagated through respective light paths leading to the scanning
means. In the present form of the invention, the optical axes of the light
paths are offset with respect to each other so that scanning spots formed
from the modulated light beams by the scanning means are offset apart from
each other along the scanning line in a scanning direction of the scanning
means.
The above form of the color exposing device does not require precise
alignment of the optical axis of the two or more light paths from the
color combining means to the scanning means, because the scanning spots
formed on the recording medium may be offset or deviated from each other
in the scanning direction. For example, the color combining means may use
a color combining prism which has selectively reflecting films for
reflecting therefrom and/or transmitting therethrough modulated light
beams such that the optical axes of the light beams travelling toward the
scanning means are parallel to each other and are offset from each other.
Alternatively, the color combining means may use reflecting mirrors for
reflecting at least one of the modulated light beams so that the optical
axes of the modulated light beams intersect each other such that the
modulated light beams irradiate the same area on each reflecting surface
of a polygon mirror of the scanning means.
Therefore, the optical components of the color exposing device according to
the above form of the invention need not be accurately assembled to assure
precise alignment of the optical axes of the modulated light beams
incident upon the scanning means. Accordingly, the exposing device can be
manufactured with high production efficiency.
In operation of the above form of the color exposing device, suitable delay
means is provided for delaying a time at which at least one of the color
image signals corresponding to the two or more colors is applied to a
corresponding at least one of the optical modulators, so that the scanning
spots of the modulated light beams for a same local spot on the surface of
said recording medium are aligned with each other at said same local spot
on the scanning line on the surface of the recording medium. For instance,
the delay means operates in a feedback fashion according to detector means
which detects an amount of spacing or offset between the adjacent scanning
spots of the modulated light beams. Namely, the detected amount represents
a required delay time for aligning the otherwise offset adjacent scanning
spots.
The light source used in the above form of the invention may comprise a
metal halide lamp, an elliptical mirror having a focal point at the metal
halide lamp, a concave lens for converting a light produced by the lamp
and reflected by the elliptical mirror, into substantially parallel rays
of light, a stop having an aperture, and a conical lens having a
translucent projection which extends through the aperture of the stop. The
conical lens receiving the parallel rays emits through the projection
thereof the radiation to be incident upon the color separation element.
The third object indicated above may be achieved according to another
aspect of the present invention, which provides a color exposing device
for imagewise scanning a photosensitive recording medium with a plurality
of signal-controlled modulated light beams corresponding to two or more
colors, respectively, the recording medium having photosensitive materials
which are sensitive to respective bands of wavelength of the light beams,
to produce color images, the color exposing device comprising: (a) feeding
means for feeding the recording medium at a predetermined constant speed
in a feeding direction; (b) time-sharing modulating means for producing
the signal-controlled modulated light beams at a predetermined interval
which is determined by a scanning pitch between adjacent scanning lines
that are spaced apart from each other in the feeding direction of the
recording medium; (c) scanning means for sequentially irradiating a
surface of the recording medium with the modulated light beams at the
predetermined time interval, along each scanning line in a scanning
direction which intersects the feeding direction; and (d) deflecting means
for deflecting the modulated light beams by different angles in the
feeding direction such that lines of scanning spots formed on the surface
of the recording medium are superimposed on each other on the same
scanning line, as the recording medium is fed at the constant speed while
the surface of the recording medium is irradiated with the deflected
modulated light beams at the predetermined time interval for each scanning
line by the scanning means.
In the color exposing device constructed as described above, the modulated
light beams are deflected in the feeding direction so that each scanning
line is irradiated with all of the modulated light beams which are
produced at the predetermined time interval while the recording medium is
continuously fed at the predetermined constant speed. Accordingly, the
scanning spots formed by all the modulated light beams for a given
scanning line are aligned with each other even though the recording medium
is continuously fed. Accordingly, the conventional experienced deviation
of the scanning spots for different colors from the nominal spot is
avoided, and the color reproduction accuracy is improved in the present
color exposing device.
Further, the present color exposing device may be obtained by modifying the
conventional counterpart, by simply adding the deflecting means for
deflecting the modulated light beams by different angles in the feeding
direction of the recording medium. Accordingly, the present device may be
available at a relatively low cost. The deflecting means may be replaced
by feeding means which is adapted to feed the recording medium
intermittently, so that the recording medium remains at the same position
until each scanning line is irradiated with all of the modulated light
beams. In this case, however, the feeding means must be constructed and
controlled so as to permit highly accurate intermittent feeding of the
recording medium with high positioning accuracy in the feeding direction.
This inevitably complicates the color exposing device, resulting in
reduced durability and operating reliability and increased cost of
manufacture of the device.
The scanning means may comprise a polygon mirror having a plurality of
plane reflecting surfaces for reflecting the modulated light beams,
respectively. The polygon mirror is rotated about an axis thereof to
deflect the reflected modulated light beams along each scanning line. In
this case, the plane reflecting surfaces of the polygon mirror may be
inclined at different angles with respect to the axis of rotation of the
polygon mirror, so that the plane reflecting surfaces serve as the
deflecting means for deflecting the reflected modulated light beams in the
feeding direction of the recording medium.
Where three signal-controlled modulated light beams corresponding to three
colors are used, the polygon mirror may have three groups of reflecting
surfaces corresponding to the three modulated light beams, each group
consisting of reflecting surfaces whose number is a multiple of three. The
scanning pitch in the feeding direction is substantially three times as
large as a feeding distance of the recording medium which corresponds to
each one of the three modulated light beams.
The color exposing device according to the above aspect of the invention
may use a light source which produces a white light including wavelength
components, and the time-sharing modulating means may comprise means for
generating a plurality of color image signals corresponding to the
wavelength components, at the predetermined time interval. In this
instance, an optical modulator is provided for modulating intensities of
the wavelength components according to the color image signals,
respectively, at the predetermined time interval. The white light may
include three wavelength components corresponding to the three primary
colors, and the color image signals consist of blue, green and red image
signals. The time-sharing modulating means may further comprise a color
filter which has three filter elements which are selectively placed in the
operating position at the predetermined time interval.
BRIEF DESCRIPTION OF DRAWINGS
The above and other objects, features and advantages of the present
invention will be better understood by reading the following detailed
description of presently preferred embodiments of the invention, when
considered in connection with the accompanying drawings, in which:
FIG. 1 is a schematic view of one embodiment of a color exposing device of
the present invention for a color imaging apparatus;
FIG. 2 is a view showing an output characteristic in terms of spectral
energy distribution of a metal halide lamp used in the color exposing
device of FIG. 1;
FIGS. 3(a), 3(b) and 3(c) are graphs illustrating spectral reflectance
values of selectively reflecting films of a color separation prism used in
the device of FIG. 1;
FIG. 4 is a view showing the selectively reflecting films of the color
separation prism indicated above;
FIG. 5 is a graph indicating spectral sensitivity of a photosensitive sheet
to blue, green and red colors of light;
FIGS. 6 and 7 are views illustrating integral optical assemblies used as an
optical modulating portion in modified embodiments of the invention;
FIG. 8 is a schematic view showing a further embodiment of the color
exposing device of this invention;
FIG. 9 is a view illustrating an optical modulating arrangement used in the
embodiment of FIG. 8, which includes delay means;
FIG. 10 is a view indicating scanning spots formed by red, green and blue
beams along a scanning line in the embodiment of FIG. 8;
FIG. 11 is a schematic view illustrating a modification of the embodiment
of FIG. 8;
FIG. 12 is a schematic view showing a still further embodiment of the color
exposing device of the present invention;
FIG. 13 is a fragmentary view of the device of FIG. 12, taken in a
direction parallel to the rotation axis of a platen roll of the device;
FIGS. 14(a), 14(b), 14(c) and 14(d) are views illustrating exposing
operations with red, green and blue beams along a line on a photosensitive
sheet while the sheet is fed;
FIGS. 15-17 are graphs indicating spectral transmittance values of red,
green and blue filter elements of a color filter used in the embodiment of
FIG. 12; and
FIG. 18 is a schematic view showing a conventional color exposing device
for a color imaging apparatus.
DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS
Referring first to FIG. 1, there is shown a color exposing device for a
color printer adapted to effect printing on a pressure-sensitive
photosensitive medium 14. The color exposing device has a light source 10,
a collimator lens 11, a scanning portion 16, and a color modulating
portion 20. The scanning portion 16 includes a polygon mirror 12 and an
f.theta. lens 13.
The light source 10 produces a white light including components having
wavelength bands corresponding toy red (R), green (G) and blue (B) colors.
The white light is converted by the collimator lens 11 into substantially
parallel rays, which are incident upon the color modulating portion 20, so
that the red, green and blue components of the light are modulated
according to respective color image signals corresponding to the red,
green and blue colors, and thus obtained three modulated light beams are
combined with each other into a composite exposing radiation, which is
incident upon the polygon mirror 12 of the scanning portion 16.
The polygon mirror 12 is rotated about its axis in the direction indicated
by arrow in FIG. 1, at a predetermined constant angular velocity, so that
the incident composite exposing radiation reflected by the polygon mirror
12 is reflected over a predetermined angular range in the plane
perpendicular to the rotation axis of the mirror 12. The deflected
exposing radiation is transmitted through the f.theta. lens and thereby
focused on the surface of the recording medium 14, such that the scanning
spot formed on the medium surface is moved along a scanning line at a
constant speed as the exposing radiation is deflected by the polygon
mirror 12 over the predetermined angular range, which covers the effective
width of the recording medium 14.
The light source 10 consists of a metal halide lamp, for example, which
produces a white light, i.e., visible spectrum of light having a spectral
energy distribution over a wavelength range between 400 nm and 700 nm, as
illustrated in FIG. 2.
The color modulating portion 20 includes a color separation prism 21,
reflecting mirrors 22, 23, 25 and 26, a color combining prism 27, and
three optical modulators 24R, 24G and 24B. As shown in FIG. 4 in detail,
the color separation prism 21 has two selectively reflecting films 28 and
29, which selectively reflect therefrom or transmit therethrough the
wavelength components of the white light W received from the collimator
lens 11. More specifically, the reflecting film 28 has a spectral
reflectance distribution as indicated in FIG. 3(a), and therefore reflects
only the component having the red wavelength band (red light beam), to the
left as indicated at R in FIG. 4. On the other hand, the reflecting film
29 has a spectral reflectance distribution as indicated in FIG. 3(b), and
therefore reflects only component having the blue wavelength band (blue
light beam), to the right, as indicated at B in FIG. 4. Further, the two
selectively reflecting films 28, 29 have a resultant spectral reflectance
distribution as indicated in FIG. 3(c). Accordingly, the remaining
component of the white light, that is, the component having the green
wavelength band (green light beam) is transmitted through the two
reflecting films 28, 29, as indicated at G in FIG. 4. Thus, the red, green
and blue components R, B, G of the white light W are separated from each
other, and propagated along respective light paths through the modulating
portion 20.
The red light beam reflected by the reflecting film 28 of the color
separation prism 21 is reflected by the reflecting mirror 22 toward the
optical modulator 24R, while the blue light beam reflected by the
reflecting film 29 is reflected by the reflecting mirror 23 toward the
optical modulator 24B.
The optical modulators 24R, 24G and 24B are disposed in the three light
paths, respectively, to modulate the intensities of the incident light
beams according to the red, green and blue image signals, respectively,
which signals are received from a suitable device. Each optical modulator
24 may use a PLZT (PbTiO.sub.3 -PbZrO.sub.3 -La.sub.2 O.sub.3) crystal
which exhibits an electro-optical effect when an image signal in the form
of a voltage signal is applied to the crystal.
The red and blue light beams modulated by the modulators 24R and 24B are
reflected by the mirrors 25, 26, toward the color combining prism 27,
respectively. The color combining prism 27 is similar in construction to
the color separation prism 21, but is differently oriented such that the
three modulated light beams are reflected by or transmitted through the
reflecting films in the downward direction as seen in FIG. 1. Thus, the
three light beams modulated by the respective modulators 24R, 24B and 24G
are combined into a composite exposing radiation (white light) by the
color combining prism 27.
The pressure-sensitive photosensitive recording medium 14 is a known
photosensitive sheet as disclosed in U.S. Pat. Nos. 4,440,846 and
4,399,209. The former patent shows a pressure-sensitive photosensitive
sheet which has a microcapsule layer and a developer layer. The
microcapsule layer consists of a multiplicity of microcapsules each
including a radiation-curable resin which is cured upon exposure to a
certain wavelength band of a light beam, and a chromogenic material or
color precursor contained in the radiation-curable resin. For example, the
microcapsule layer consists of three groups of microcapsules whose
radiation-curable resin are sensitive to the three primary colors of
light, i.e., red, green and blue light beams, and whose chromogenic
materials are capable of reacting with a developing material of the
developer layer, to form yellow, magenta and cyan. The microcapsules are
ruptured as by presser rolls, according to the mechanical strength which
varies with the amount of exposure to the light beams, and the chromogenic
materials which come out of the radiation-curable resin react with the
developing material.
U.S. Pat. No. 4,399,209 shows a photosensitive sheet having a microcapsule
layer as described above, which is used in combination with a separate
developer sheet which has a developer layer including the developing
material.
The present color exposing device is applicable to a photosensitive sheet
of either of the two types described above. FIG. 5 shows the spectral
sensitivity distribution of the pressure-sensitive photosensitive medium
14 used in the present embodiment. It will be understood that the
photosensitive medium 14 has maximum values of sensitivity to a blue light
beam having a wavelength of about 450 nm, a green light beam having a
wavelength of about 550 nm, and a red light beam having a wavelength of
about 650 nm.
While the color modulating portion 20 of the color exposing device
described above uses the optical components which are structurally
separate from each other, the color modulating portion 20 may be
constituted by a single integrated optical component or assembly as shown
in FIGS. 6 and 7.
In the integrated optical modulator of FIG. 6, a color separation prism 30
has two selectively reflecting films which reflect the red and blue
wavelength components of an incident white light and transmit the green
wavelength component. The red and blue wavelength components reflected by
the prism 30 are reflected by inclined surfaces of the prism 30 which are
parallel to the reflecting films. The modulator also has a color combining
prism 31, and an array of three optical modulators 24R, 24G and 24B
disposed between the two prisms 30, 31. The red, green and blue wavelength
components are transmitted through the respective optical modulators 24R,
24G and 24B, and the modulated components (modulated light beams) are
received by the color combining prism 31. The red and blue light beams
modulated by the modulators 24R and 24B are reflected by inclined surfaces
of the prism 31 parallel to the reflecting films, which reflect the
incident red and blue light beams toward the polygon mirror 12 of the
scanning portion 16.
It will be understood that the integrated optical modulator of FIG. 6
utilizes the inclined outer surfaces of the two prisms 30, 31 as
reflecting mirrors which define the light paths for the red and blue light
beams. Thus, the modulator of FIG. 6 does not use exclusive reflecting
mirrors (22, 23, 25 and 26) as used in the preceding embodiment of FIG. 1.
In the integrated optical modulator of FIG. 7, a color separation prism 32
has a first selectively reflecting film 33 for transmitting only the green
wavelength component of the incident white light and reflecting the red
and blue wavelength components in the right direction (as viewed in FIG.
7), a second selectively reflecting film 34 for reflecting only the blue
wavelength component and transmitting the red wavelength component in the
right direction, and a third selectively reflecting film 35 for reflecting
the red wavelength component in the downward direction (as viewed in FIG.
7). The first reflecting film 33 has a spectral reflectance distribution
as shown in FIG. 3(c), and the second reflecting film 34 has a spectral
reflectance distribution as shown in FIG. 3(b). The third selectively
reflecting film 35 reflects all wavelength components of the incident
light. The modulator of FIG. 7 also has a color combining prism 36 which
has a fourth, a fifth and a sixth selectively reflecting film 37, 38, 39,
which have the same spectral reflectance characteristics as the third,
second and first reflecting films 35, 34, 33, respectively. Between the
two prisms 32, 36, there is disposed an array of the three optical
modulators 24R, 24G and 24B for modulating the respective red, green and
blue wavelength components.
While the integrated optical modulator of FIG. 6 has a total of eight
reflecting surfaces (including the reflecting films), the integrated
optical modulator of FIG. 7 has a total of six reflecting surfaces (33-35
and 37-39). In this respect, the modulator of FIG. 7 is available at a
comparatively reduced cost.
While the light source 10 and the pressure-sensitive photosensitive
recording medium 14 has the spectral energy and sensitivity
characteristics as indicated in FIGS. 2 and 5, respectively, the color
exposing device according to the present invention may use a light source
and a photosensitive recording medium which have spectral energy and
sensitivity characteristics different from those of FIGS. 2 and 5.
In the above embodiments of FIGS. 1, 6 and 7, the optical modulators 24R,
24G and 24B are electro-optic modulators, these electro-optic modulators
may be replaced by acousto-optic modulators or liquid crystal shutters.
Referring next to FIGS. 8-10, there will be described a further embodiment
of the present invention. In the interest of brevity and simplification,
the same reference numerals as used in the first embodiment of FIG. 1 will
be used in FIGS. 8 and 9 to identify the corresponding components.
The color exposing device of the present embodiment uses a light source
device 40 which includes a metal halide lamp 41. Like the white light
source 10 of the first embodiment, the metal halide lamp 41 produces a
white light and has a spectral energy distribution as indicated in FIG. 2.
The white light produced by the lamp 41 is reflected by an elliptical
mirror 42 and the reflected light is incident upon a concave lens 44. The
elliptical mirror 42 has a first focal point at the point of emission of
the white light of the lamp 41, and a second focal point which is located
between the first focal point (lamp 41) and the concave lens 44. The white
light incident upon the concave lens 44 is converted into substantially
parallel rays, which are converged by a conical lens 46. The conical lens
46 has a translucent projection 50 which extends through an aperture
formed through a stop 48. In this arrangement, the converged beam is
radiated from the projection 50 toward the collimator lens 11. The stop 48
is held in contact with the end face of the body of the conical lens 46
from which the projection 50 extends. The stop 48 functions to stop a
portion of the beam which would be otherwise emitted from the peripheral
part of the end face of the lens 46. The radiation incident upon the
collimator lens 11 is converted into substantially parallel rays, which
are incident upon the color modulating portion 20.
The color modulating portion 20 has the optical modulators 24B, 24G and 24R
using electro-optic PLZT crystals. As shown in FIG. 9, these optical
modulators 24B, 24G and 24R are adapted to receive color image signals in
the form of voltage signals generated from respective voltage applying
circuits 61, 62, 63 which correspond to the primary colors of light, blue,
green and red. The blue, green and red wavelength components of the light
incident upon the color modulating portion 20 are separated by the prism
21, and are modulated by the respective modulators 24B, 24G and 24R
according to the voltage signals from the respective circuits 61-63.
While the color modulating portion 20 of the present embodiment of FIGS. 8
and 9 is similar in construction to that of the embodiment of FIG. 1, the
reflecting mirrors 25 and 26 are oriented such that the optic axes of the
red and blue light beams reflected by the color combining prism 27 are
parallel to each other but are slightly offset or spaced apart from each
other in the direction perpendicular to the optic axes. Namely, it is not
necessary to accurately position the reflecting mirrors 25, 26 so that the
optic axes of the red, green and blue light beams of the composite
exposing radiation from the prism 27 are accurately aligned with each
other.
In the present arrangement of the color modulating portion 27, the scanning
spots 52B, 52G and 52R formed on the surface of the recording medium 14 by
irradiation with the respective blue, green and red light beams reflected
from the polygon mirror 12 are located on a scanning line and are slightly
offset from each other in the scanning direction, as indicated in FIG. 10.
The scanning direction is perpendicular to the rotation axis of the
polygon mirror 12. In other words, the reflecting mirrors 25 and 26 are
oriented such that the scanning spots 52B, 52G and 52R are located on the
scanning line in mutually offset relation with each other as indicated in
FIG. 9. This arrangement does not require precise adjustment of the color
modulating portion 20 for accurate alignment of the blue, green and red
scanning spots 52B, 52G and 52R with each other.
In operation of the color exposing device, however, all of the three
scanning spots 52B, 52G, 52R for a given local spot on the relevant
scanning line should be formed at that given local point, or aligned with
each other. To this end, a first and a second delay circuit 64, 65 are
connected to the respective voltage applying circuits 62, 63 for the
modulators 24G and 24R for the green and red light beams. The first and
second delay circuits 64, 65 function to delay the times at which the
voltage signals (green and red color image signals) are applied to the
respective modulators 24G, 24R, so that the scanning spots 52G and 52R are
located on the corresponding scanning spot 52B. The delay times of the
delay circuits 64, 65 are proportional to the spacings between the
scanning spot 52B and the scanning spots 52G, 52R, respectively, in the
scanning direction. In this respect, it is noted that the scanning speed
or the speed of deflecting the composite exposing radiation by the polygon
mirror 12 through the f.theta. lens 13 is constant over the entire length
of the scanning line. The required delay times may be obtained by
experimentally measuring the spacings between the scanning spots 52 when
the delay circuits 64, 65 are placed in the inoperative position.
The present embodiment of FIGS. 8-10 permits sufficiently high accuracy of
reproduction of color images, owing to the provision of the delay circuits
64, 65, in spite of relatively rough positioning or adjustment of the
reflecting mirrors 25, 26, which allows for relatively easy assembling of
the color modulating portion 20.
In the embodiment of FIG. 8, the optical axes of the three modulated light
beams of the composite exposing radiation from the color combining prism
27 are parallel to each other and are offset from each other. However, the
optical axes of the three light beams may intersect each other as
indicated in FIG. 11.
More specifically, the color exposing device of the embodiment of FIG. 11
uses two reflecting mirrors 66, 67 for reflecting the blue and red
wavelength components reflected by the color separation prism 21. These
two mirrors 66, 67 are oriented such that the optical axes of the three
modulated light beams intersect each other and such that the three
modulated light beams irradiate the same area on each reflecting surface
of the polygon mirror 12. In this arrangement, too, the scanning spots
52B, 52G and 52R are offset from each other along a scanning line as
indicated in FIG. 10, if the delay circuits 64, 65 are not in the
operative position. In the present embodiment of FIG. 11, a color
combining prism as used in the preceding embodiments of FIGS. 1, 6, 7 and
8 is not provided, and the color modulating portion of the device may be
accordingly simplified and available at a reduced cost.
For accurate alignment of the three scanning spots 52B, 52G and 52R with
each other by the operations of the delay circuits 64, 65, it is desirable
that suitable detector means is provided to detect the relative positions
of the optical axes of the three modulated light beams (scanning spots 52)
near the surface of the recording medium 14, so that the delay times of
the delay circuits 64, 65 required to accurately align the scanning spots
52 on the medium surface. In this case, the output of the detector means
is applied to the delay circuits 64, 65 to control the timings of
application of the green and red color image signals (voltage signals) to
the respective modulators 24G and 24R in a feedback fashion. This
arrangement permits compensation for a variation in the relative positions
of the three scanning spots 52B, 52G and 52R which would be formed without
the use of the delay circuits 64, 65. This variation may occur due to a
change in the operating temperature or a variation in the relative
position of the optical components of the color modulating portion 20
during use of the color exposing device.
The color modulating portion 20 of FIG. 8 may also be replaced by a single
integrated optical component or assembly as shown in FIGS. 6 and 7.
Reference is now made to FIG. 12, which shows a still further embodiment of
the present invention. In the figure, reference numeral 70 denotes a metal
halide lamp which produces a white radiation L having a wavelength band of
about 400-700 nm. Like the metal halide lamps 10 and 41 used in the
embodiments of FIGS. 1 and 8, the lamp 70 has a spectral energy
distribution as indicated in FIG. 2. The white radiation L is transmitted
through a collimator lens 72, and is incident upon an electro-optical
modulator 74 using a PLZT crystal. The modulator 74 modulates the
intensity of the incident radiation according to color image signals SC
received from a suitable external device such as a color camera. The color
image signals SC consist of a red image signal R, a green image signal G
and a blue image signal B, which represent the proportions of red, green
and blue colors of an image at each local spot along each scanning line on
a recording medium in the form of a pressure-sensitive photosensitive
sheet 84 which is fed by rotation of a platen roll 86. The sheet 84 is
similar to the recording medium 14 used in the preceding embodiments. As
described below, the red, green and blue image signals R, G, B for each
scanning line are sequentially applied to the optical modulator 74, as the
recording medium 84 is fed. Namely, the red image signal R is first
applied to the modulator 74 for exposing the recording medium 84, to form
a line of latent red images along a scanning line, and then the green and
blue image signals are successively applied to the modulator 74 to form
respective lines of latent green and blue images along the same scanning
line. Thus, the three scanning operations are effected along the same
scanning line, one after another, to form a line of latent images for full
color imaging along the relevant scanning line according to the
sequentially applied color image signals R, G, B. Since a page of images
to be reproduced on the recording medium consists of two or more lines of
images, the above color scanning or exposing operation cycle is repeated
according to a batch of color image signals R, G, B.
The white radiation color-modulated by the optical modulator 74 as
described above is incident upon a disc-like color filter 76 which is
rotated about an axis thereof and which is circumferentially divided into
three filter elements, i.e., red filter element R, green filter element G
and blue filter element B. Each of these three filter elements R, G, B
covers a 120.degree. division of the circumference of the filter 76, and
is selectively and sequentially brought into the operative position, by
rotation of the filter 76, in accordance with the currently applied color
image signal R, G, B. The filter elements R, G, B transmit the respective
red, green and blue wavelength components of the incident white radiation,
respectively, when the elements R, G, B are selectively placed in the
operative position aligned with the light path passing through the filter
76. The spectral transmittance distributions of these filter elements R,
G, B are illustrated in the graphs of FIGS. 15, 16 and 17, respectively.
The wavelength components which are transmitted through the color filter 76
are incident upon a polygon mirror 78, as three modulated light beams LR,
LG, LB. The polygon mirror 78 is a hexagonal prism having six plane
reflecting surfaces 80a-80f. These six reflecting surfaces 80a-80f are
classified into three groups or sets, a first set consisting of the
surfaces 80a, 80d, a second set consisting of the surfaces 80b, 80e, and a
third set consisting of the surfaces 80c, 80f. The first set 80a, 80d is
used to reflect the red light beam LR, the second set 80b, 80e to reflect
the green light beam LG, and the third set 80c, 80f to reflect the blue
light beam LB. As the polygon mirror 78 is rotated about the axis l at a
predetermined constant angular velocity, the light beams LR, LG, LB are
reflected by the respective reflecting surfaces 80a, 80d; 80b, 80e; 80c,
80f, and the reflected light beams LR, LG, LB are deflected over a
predetermined angular range in a plane perpendicular to the rotation axis
of the polygon mirror 78 (in a plane parallel to the rotation axis of the
platen roll 86). While the filter element R is placed in the operative
position, for example, the modulated light beam LR is reflected and
deflected in the above-indicated plane, by the reflecting surface 80a or
80d.
The reflected and deflected light beams LR, LG, LB are transmitted through
an f.theta. lens 82 and converged on the surface of the photosensitive
recording medium 84 on the platen roll 86. The f.theta. lens 82 permits
the light beams LR, LG, LB to be deflected at a constant speed over the
predetermined angular range, in the scanning direction parallel to the
axis of the platen roll 86. As a result, a scanning spot S formed on the
recording medium 84 by each modulated light beam is moved in the scanning
direction at the constant speed over the entire width of the recording
medium 84.
The pressure-sensitive photosensitive recording medium 84 is continuously
fed by the platen roll 86 at a predetermined speed, in a feeding direction
which is perpendicular to the scanning direction. That is, the rotation
axis of the platen roll 86 is parallel to the scanning direction in which
the modulated light beams LR, LG, LB are deflected by the rotation of the
polygon mirror 78. The scanning or exposing operations with the three
modulated light beams LR, LG, LB are effected for each of parallel
scanning lines parallel to the rotation axis of the platen roll 86, so
that lines of latent images are formed for one page of image, as the
recording medium 84 is continuously fed.
Referring to FIG. 13, there are shown the polygon mirror 78, f.theta. lens
82, recording medium 84 and platen roll 86 as seen in the direction
parallel to the rotation axis of the platen roll 86. As indicated in solid
line in FIG. 13, the plane reflecting surfaces 80b, 80e of the polygon
mirror 78 for deflecting the modulated green light beam LG in the
direction parallel to the rotation axis of the platen roll 86 are formed
parallel to the rotation axis l of the polygon mirror 78. However, the
plane reflecting surfaces 80a, 80d for reflecting the modulated red light
beam LR are inclined relative to the rotation axis l of the polygon mirror
78 by an angle .alpha., as indicated in dashed line in FIG. 13. Further,
the plane reflecting surfaces 80c, 80f for deflecting the modulated blue
light beam LB are inclined relative to the rotation axis l by the same
angle as the reflecting surfaces 80a, 80d, but in the opposite direction
with respect to the reflecting surfaces 80a, 80d, as indicated in one dot
chain line in FIG. 13. In this arrangement, a scanning spot SR formed on
the medium 84 by the red light beam LR is spaced apart by a distance
.delta. from a scanning spot SG formed by the green light beam LG, in the
direction opposite to the feeding direction of the medium 84, if the
medium 84 was irradiated by the light beams LR and LG at the same time and
if the medium 84 is not fed. Similarly, a scanning spot SB formed by the
blue light beam LB is spaced apart by the same distance .delta. from the
scanning spot SG, in the feeding direction of the medium 84.
The relationship between the inclination angle .alpha. of the reflecting
surfaces 80c, 80f, 80b, 80e and the spacing distance .delta. of the
scanning spots SG, SR, SB is represented by the following equation (1):
tan 2.alpha.=.delta./f (1)
where, f: focal length of the f.theta. lens 82
The angle .alpha. is determined based on the rotating speed and diameter of
the platen roll 86 and other factors, so that the distance of feed of the
recording medium 84 in the direction parallel to the rotation axis of the
polygon mirror 78 during each scanning operation by the corresponding
reflecting surface 80 is equal to the spacing distance .delta.. The
spacing distance 6 or the corresponding feed distance of the medium 84 is
selected to be almost equal to one-third (1/3) of the scanning spots S of
the modulated light beams LR, LG, LB. If the scanning spots S have a
diameter of 80 .mu.m and the f.theta. lens 82 has a focal length f of 100
mm, the inclination angle .alpha. of the reflecting surfaces 80c, 80f,
80b, 80e is about 29" (about 0.008.degree.), according to the equation
(1).
FIGS. 14(a) through 14(d) illustrate the absolute scanning or exposing
positions of the three modulated light beams LR, LG, LB, and the feeding
movements of the recording medium 84, each movement by the distance
.delta. after each scanning operation. While the absolute scanning or
exposing positions of the three light beams LR, LG, LB are offset from
each other in the right direction as seen in FIGS. 14, the same area on
the recording medium 84 is exposed to the three light beams, since the
medium 84 is fed by the incremental distance .delta. during one scanning
or exposing operation with each light beam LR, LG, LB. Namely, the lines
of the scanning spots SR, SG, SB formed on the medium surface are
superposed on each other on the same scanning line on the medium surface.
Further, since the diameter of the scanning spots S is almost three times
the feeding distance .delta. (spacing distance between the absolute
positions of the adjacent scanning spots SR, SG, SB), the feeding of the
medium 84 by the total distance of 3.delta. to effect the three scanning
operations with the three light beams LR, LG, LB permits the medium 84 to
be positioned for the next scanning cycle for the next line of images.
Thus, the lines of the scanning spots formed on the medium surface with
the repeated scanning cycles for successive lines of images cover the
medium surface, without gaps between the lines of the scanning spots
(lines of images). It is noted that the diameter of the spots S defines or
determines the scanning pitch which is a distance between adjacent
scanning lines (lines of images) on the medium 84. The feed distance
.delta. is one-third (1/3) of the scanning pitch.
It will be understood from the foregoing description of the present
embodiment that the plane reflecting surfaces 80a-80f of the polygon
mirror 78 serve not only as scanning means for deflecting the light beams
LR, LG, LB in the scanning direction perpendicular to the rotation axis l
of the mirror 78, but also as deflecting means for permanently deflecting
the light beams LR, LG, LB in the feeding direction parallel to the
rotation axis l, so that the lines of the scanning spots SR, SG, SB formed
on the medium surface are superimposed on each other or aligned with the
same scanning line on the medium surface, as the recording medium 84 is
continuously fed at the constant speed while the medium surface is
irradiated with the light beams at the predetermined time interval.
Accordingly, each scanning line on the medium surface is scanned by the
three light beams LR, LG, LB at different times, without the lines of
scanning spots SR, SG, SB being offset in the feeding direction, whereby
the accuracy of reproduction of images is improved although each scanning
cycle consisting of three scanning operations with the three light beams
is effected while the recording medium 84 is continuously fed at the
constant speed.
The above advantage is obtained by simply forming the polygon mirror 78
such that the reflecting surfaces 80a, 80d, 80c, 80e are inclined by the
angle .alpha. with respect to the rotation axis l as described above. No
exclusive components or no modifications of the other components are
required to offset the absolute positions of the scanning spots SR, SG, SB
relative to the circumference of the platen roll 86. Therefore, the above
arrangement may be readily applied to a conventional color exposing device
using a polygon mirror. The present color exposing device is similar in
construction and available at a lower cost, than a device wherein the
platen roll (86) is held stationary while a scanning cycle with the three
light beams is completed.
Although the polygon mirror 78 has the six plane reflecting surfaces
80a-80f, the number of the reflecting surfaces 80 may be suitable changed,
provided that the number is a multiple of the number of the modulated
light beams, i.e., a multiple of 3. That is, the polygon mirror 78 may
have only three reflecting surfaces 80, or nine or twelve reflecting
surfaces 80.
In the embodiment of FIGS. 12 and 13, the polygon mirror 78 for scanning in
the direction perpendicular to the feeding direction also serves as the
means for permanently deflecting the light beams LR, LG, LB in the feeding
direction. However, the permanently deflecting means may be provided by a
member or members separate from the polygon mirror 78.
The electro-optical modulator 74 may be replaced by an acousto-optical
modulator or a liquid crystal shutter which is operated according to color
image signals. Further, the optical modulator 74 may be disposed between
the color filter 76 and the polygon mirror 78, so that the wavelength
components of the white radiation that are passed through the filter 76
are modulated by the modulator 74.
Although the recording medium 84 is fed by the platen roll 86, a planar
platen may be used so that the medium 84 is fed flat while being supported
by the planar platen. Further, the beam scanning direction of the polygon
mirror 78 and the feeding direction of the recording medium 84 need not be
perpendicular to each other, but may intersect each other at a suitable
angle. For example, the scanning direction may be slightly inclined with
respect to the rotation axis of the platen roll 86.
While the present invention has been described in the presently preferred
embodiments with a certain degree of particularity, it is to be understood
that the invention is not limited to the details of the illustrated
embodiments, but may be otherwise embodied, with various changes and
modifications other than those indicated above.
For example, the microcapsules of the pressure-sensitive photosensitive
recording medium 14, 84 may use a resin which is softened rather than
cured, upon exposure to light.
The light source or lamp 10, 41, 70 may have a spectral energy distribution
characteristic different from that indicated in FIG. 2. The recording
medium 14, 84 may have a spectral sensitivity characteristic different
from that indicated in FIG. 5. Further, the selectively reflecting films
28, 29 used in the color modulating portion 20 of the embodiments of FIGS.
1 and 8 may have spectral reflectance characteristics different from those
indicated in FIGS. 3(a), 3(b) and 3(c), and the filter elements of the
color filter 76 used in the embodiment of FIG. 12 may have spectral
transmittance characteristics different from those of FIGS. 15-17.
The invention may be embodied with various other changes, modifications and
improvements, which may occur to those skilled in the art, without
departing from the spirit and scope of the invention defined in the
following claims.
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